tailieunhanh - ADVANCED MECHANICS OF COMPOSITE MATERIALS Episode 14

Tham khảo tài liệu 'advanced mechanics of composite materials episode 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 442 Advanced mechanics of composite materials Fig. . For this type of loading Nx 2 pR Ny pR Nxy 0 where Nx and Ny are the circumferential and axial stress resultants respectively p the internal pressure and R is the cylinder radius. Thus we have ny 2 and Ấ 1 3. Since Nxy 0 the structure of the laminate is symmetric with respect to the cylinder meridian and Eqs. - can be reduced to 3pR h 2ơ 1 k hi 3cos2 ội - 1 0 i 1 Comparing Eq. with the corresponding expression for the thickness of a metal pressure vessel which is hm pR ỡ we can see that the thickness of an optimal composite vessel is times more than hm. Nevertheless because of their higher strength and lower density composite pressure vessels are significantly lighter than metal ones. To show this consider pressure vessels with radius R 100 mm made of different materials and designed for a burst pressure p 20 MPa. The results are listed in Table . As can be seen the thickness of a glass-epoxy vessel is the same as that for the thickness of a steel vessel because the factor in Eq. is compensated by the composite s strength which is times greater than the strength of steel. However the density of a glass-epoxy composite is much lower than the density of steel and as a result the mass of unit surface area of the composite vessel is only 27 of the corresponding value for a steel vessel. The most promising materials for pressure vessels are aramid and carbon composites which have the highest specific tensile strength see Table . Consider Eq. which shows that there can exist an infinite number of optimal laminates with one and the same thickness specified by Eq. . Table Parameters of metal and composite pressure vessels. Parameter Material Steel Aluminum Titanium Glass- epoxy Carbon- epoxy Aramidepoxy Strength õ Ỡ1 MPa 1200 500 900 1800 2000 2500 Density p g cm3 Thickness of the vessel hm h mm Mass .